Recycling of electronic and electrical equipment waste by soft chemistry: when cutting edge science becomes low-tech.

Deep eutectic solvents are a recently developed class of liquids obtained by mixing an organic hydrogen bond donor and hydrogen bond acceptor, leading to a phase with a melting point much lower than that of the two components.

The most frequently used hydrogen bond acceptor is hydroxyethyltrimethylammonium (choline) chloride, but several quaternary ammonium salts can be used. Several hydrogen bond donors are used together with choline chloride, such as urea, glycerol, and carboxylic acid, ... All those compounds are relatively cheap and innocuous.

This work was carried out in two successive collaborative projects with Burkina Faso, aimed at safe small scale processes for recovery of precious and critical metals from WEEE (Waste of electronic and electrical equipment). Several solvents based on choline chloride were used to leach metals from printed circuit boards and lithium ions batteries, after dismantling and appropriate preparation of the WEEE. It proved possible to transfer most of the interesting metals in the leachate, thus providing the basis for a low-tech, low-CAPEX method for the local recycling of critical and precious metals. Current work carried out by a local team in Burkina Faso aims at industrialising the developed methods, and combining them with recovery from the deep eutectic solvent by electroplating (developed by other colleagues involved in the same project) to institute a full local recycling stream, replacing the current semi-artisanal methods that rely on toxic media such as cyanide or mercury for the leaching of precious metals.